Simplifying the process of generating filled contours is beneficial in applications such as printing which are based on font outlines. The traditional method is to use a parametric cubic spline algorithm to generate points along the curve. These points are saved, and used as the vertices of an approximating polygon that represents the bounded fill region to some specified degree of accuracy. The approximating polygon is then filled using a method such as the edge flag algorithm.
The polygon fill is performed in two steps: first, a list is made of the edges on each horizontal scan line of the raster; and second, for each scan line, a pair of edges defines a horizontal span of the filled region. Thus, in the traditional method, three steps are required, namely:
1. Generating vertices of approximating polygon by using a cubic spline (or DDA) algorithm;
2. Converting each straight edge of the generated polygon into a list of edges on a per-scan-line basis; and
3. Drawing each pair of edges on a scan line as a horizontal span belonging to the filled region using a parity or non-zero winding number fill algorithm.
In order to reduce computing time and to generate more accurate results, a system is required which reduces the number of steps required for each curve generation.